Apparatus for magnetically detecting faults in metal bodies utilizing a multiphase generator to generate a rotating field in the body

Abstract

An improved device for magnetically detecting and locating defects in metal bodies such as shafts, tubes, strips, sheets etc., in which a multiphase generator is used to generate a traveling field such as a rotating or linearly traveling field in the body being tested and in which means are provided to sense any assymetry in the resulting magnetic field resulting from eddy currents induced in the object such as to permit determining the location and nature of the fault from the electrical signals obtained.

What is claimed is: 
     
       1. Apparatus for testing metal bodies comprising: a. a first y-connected multi-phase generator;   b. a first plurality of y-connected transducer coils comprising at least one coil per phase of the multi-phase generator arranged symmetrically relative to a metal body to be tested, said coils coupled to the phase outputs of said generator such as to induce a moving field in said body when fed with a multi-phase current therefrom; and   c. a second plurality of y-connected transducer coils comprising at least one coil per phase of the multi-phase generator arranged symmetrical relative to said metal body to be tested, said coils coupled to the phase outputs of said generator such as to induce a moving field in said body whose direction is opposite to that of the moving field generated by said first plurality of y-connected transducer coils when fed with a multi-phase current from said multi-phase generator, said second plurality of y-connected transducer coils being located at a section of said metal body different from the section where said first plurality of y-connected transducer coils are located; and   d. means to detect variations in the electrical field generated by said transducer coils which occur when faults and irregularities in the body being tested are encountered comprising 1. First and second transducer coils located adjacent to said metal body between said first and second pluralities of transducer coils and connected in series;   2. a transformer having first and second secondary windings in series and a single primary winding;   3. first and second impedances coupling said first and second transducer coils in series to said first and second secondary windings in series;   4. means to detect an unbalance between the point at which said first and second transducer coils are connected in series and the point at which said first and second secondaries are connected in series; and   5. means to induce a voltage on the primary of said transformer.